This invention relates to aromatic acetylene compounds and their utilization as ablative materials for re-entry vehicles. In a more particular aspect, this invention relates to the synthesis of diethynylbenzene-ethynylpyrene copolymers and their use as high char yielding matrix resins for carbon-carbon composites.
The increased use and interest in the operation of re-entry vehicles has generated a considerable research effort in an attempt to develop structural materials that exhibit high strength and resistance to the stresses and strains encountered by space vehicles during their re-entry regime. Rocket and missile components, such as turbine blades, nozzles, vanes, partitions, and especially nose cones, are very vulnerable to the stress and strain encountered during their re-entry environment. These components require structural materials capable of surviving those stresses and the elevated temperatures occurring during re-entry.
Graphite carbon, in the form of a carbon-carbon composite, using pitch as a resinous matrix, has been found to be useful in fabricating structural components. These materials possess many of the characteristics required by structural elements subjected to the stress of a high temperature re-entry environment. The carbon-carbon materials have proven to be especially effective for nose tip applications and show good thermal stress performance. Unfortunately, these materials often times do not show sufficient mechanical strength, disclose unpredicted anomalies in their ablation characteristics, and require expensive, high pressure processing techniques.
With the present invention, however, it has been found that carbon-carbon composites having superior re-entry characteristics can be produced simply and easily by utilizing a novel aromatic acetylene copolymer as a high char yielding matrix resin for the carbon-carbon composite in lieu of the previously used pitch. The novel copolymer matrix resin is derived by effecting the copolymerization of a mixture of diethynylbenzene and ethynylpyrene.
The reaction mechanism does not require high pressure processing parameters and the resulting copolymer chars easily when utilized as a matrix impregnant for graphite fibers. It easily wets the graphite fibers and penetrates into the pores of the fibers.
The present invention replaces the ill defined, variable composition pitches utilized heretofore as an impregnant and matrix resin for the carbon-carbon composites produced heretofore. The pitches are invariably contaminated with S, O, N, P, ash, and other materials. In addition, the pitch is not homopolymerizable, therefore, it can exude from the impregnated woven carbon composites during processing and, by virtue of the fact that it is not comprised strictly of aromatic hydrocarbon, has a lower carbon content than the material of the instant invention. As a consequence, pitch has a much lower char yield. The instant invention provides processing simplification far beyond the current state of the art pitch and provides more dependable performance characteristics for the carbon-carbon composite products derived therefrom.